Magnetic resonance imaging of radiation-induced thymic atrophy as a model for pathologic changes in acute feline immunodeficiency virus infection.

The development of a protocol to reproducibly induce thymic atrophy, as occurs in feline immunodeficiency virus (FIV) infection and other immunosuppressive diseases, and to consistently estimate thymic volume, provides a valuable tool in the search of innovative and novel therapeutic strategies. Magnetic resonance imaging (MRI) using the short tau inversion recovery (STIR) technique, with fat suppression properties, was determined to provide an optimized means of locating, defining, and quantitatively estimating thymus volume in young cats. Thymic atrophy was induced in four, 8-10-week-old kittens with a single, directed 500 cGy dose of 6 MV X-rays from a clinical linear accelerator, and sequential MR images of the cranial mediastinum were collected at 2, 7, 14, and 21 days post irradiation (PI). Irradiation induced a severe reduction in thymic volume, which was decreased, on average, to 47% that of normal, by 7 days PI. Histopathology confirmed marked, diffuse thymic atrophy, characterized by reduced thymic volume, decreased overall cellularity, increased apoptosis, histiocytosis, and reduced distinction of the corticomedullary junction, comparable to that seen in acute FIV infection. Beginning on day 7 PI, thymic volumes rebounded slightly and continued to increase over the following 14 days, regaining 3-35% of original volume. These findings demonstrate the feasibility and advantages of using this non-invasive, in vivo imaging technique to measure and evaluate changes in thymic volume in physiologic and experimental situations. All experimental protocols in this study were approved by the Institutional Animal Care and Use Committee (IACUC) at Auburn University.

Proliferative sparganosis in a dog.

CASE DESCRIPTION: A 21-month-old spayed female Border Collie was examined because of progressive right forelimb lameness, signs of pain, and subcutaneous edema. The dog lived in a fenced yard in Tampa, Fla, that contained a small area of marshy terrain. CLINICAL FINDINGS: The subcutis and intermuscular fascia contained multiple cystic cavities filled with larval cestodes (plerocercoids or spargana) and cloudy red fluid. Parasites were identified morphologically and by DNA sequence analysis as pseudophyllidean cestodes, most likely Sparganum proliferum. The dog developed a progressively worsening fever, dyspnea, mature neutrophilia, and hypoproteinemia. Septic pleuritis and peritonitis complicated the later stages of the disease. TREATMENT AND OUTCOME: Treatment with praziquantel, fenbendazole, and nitazoxanide failed to control the proliferation and dissemination of larval cestodes. The dog was euthanatized after 133 days of treatment. At necropsy, numerous parasitic tissue cysts were present in the subcutis and intermuscular fascia; these cysts were most abundant in the soft tissues of the forelimbs and cervical musculature. The pleural and peritoneal cavities contained multiple larval cestodes and were characterized by neutrophilic inflammation and secondary bacterial infection. CLINICAL RELEVANCE: Findings indicated that clinical signs associated with proliferative sparganosis in dogs may be rapidly progressive and that the condition may be refractory to antiparasitic treatment. Veterinarians should be aware of this zoonotic, water-borne agent.

Loss of naïve (CD45RA+) CD4+ lymphocytes during pediatric infection with feline immunodeficiency virus.

Feline immunodeficiency virus (FIV) infection of cats is an animal model for the pathogenesis of CD4+ lymphopenia and thymus dysfunction in HIV-infected humans. Recently, a monoclonal antibody (755) was reported to recognize the feline homologue to CD45RA, allowing the enumeration of naïve T cells in cats. We tested the hypothesis that pediatric FIV infection would be associated with a selective loss of naïve CD4+ lymphocytes by inoculating newborn cats with a pathogenic clone of FIV (JSY3) or a related clone with an inactive ORF-A gene (JSY3-DeltaORFA), and compared the data to age-matched uninfected control cats. Both FIV inocula were associated with a reduction in the CD4-CD8 ratio (p=0.01), which was attributable to a disproportionate loss of naïve CD4+ cells (p=0.01) vs. naïve CD8+ cells. Therefore, the reduced CD4:CD8 ratio in FIV-infected juvenile cats is associated with a selective depletion of naïve CD4+ cells from the blood.